Nickel-base superalloy articles and method for producing the same

ABSTRACT

A nickel-base superalloy compacted, fully dense article produced by elevated-temperature compacting of prealloyed powder particles consisting essentially of, in weight percent, carbon 0.50 max., chromium 10 to 16, cobalt 7 to 11, molybdenum up to 5, tungsten up to 7, columbium up to 5, tantalum up to 5, hafnium up to 5, with the total content of tungsten + columbium + tantalum + hafnium within the range of 1.0 to 12.0, vanadium up to 5, titanium 1 to 5, aluminum 2 to 6, boron 0.001 to 0.03, zirconium 0.01 to 0.20, balance essentially nickel, said article being characterized by the absence of minor phase concentrations at prior powder-particle boundaries.

United States Patent [1 1 M011 et a1.

[ NICKEL-BASE SUPERALLOY ARTICLES AND METHOD FOR PRODUCING THE SAME [75] Inventors: John H. M011; August Kasak, both of Pittsburgh, Pa.

[73] Assignee: Crucible Inc., Pittsburgh, Pa. 22 Filed: Sept. 11, 1972 [21] Appl. No.: 288,234

[52] US. Cl. 29/182; 75/171; 75/226 [51] Int. Cl C22c 19/00; C22c 1/04 [58] Field of Search 29/182; 75/226, 171

[56] References Cited UNITED STATES PATENTS 2,920,956 l/196O Nisbet et al 75/171 3,343,950 9/1967 Richards ct al. 75/171 3,390,023 6/1968 Shira 75/171 X 3,459,545 8/1969 Bieber et a1, 75/171 3,524,744 8/1970 Parikh 75/171 3,561,955 2/1971 Wheaton. 75/171 3,615,376 10/1971 Ross 75/171 [451 Sept. 2, 1975 Primary ExaminerCarl D. Quarforth Assistant ExaminerR. E. Schafer [5 7 ABSTRACT A nickel-base superalloy compacted, fully dense article produced by elevated-temperature compacting of prealloyed powder particles consisting essentially of, in weight percent, carbon 0.50 max., chromium 10 to 16, cobalt 7 to 11, molybdenum up to 5, tungsten up to 7, columbium up to 5, tantalum up to 5, hafnium up to 5, with the total content of tungsten columbium tantalum hafnium within the range of 1.0 to 12.0, vanadium up to 5, titanium 1 to 5, aluminum 2 to 6, boron 0,001 to 0.03, zirconium 0.01 to 0.20, balance essentially nickel, said article being characterized by the absence of minor phase concentrations at prior powder-particle boundaries.

4 Claims, 6 Drawing Figures PATENTED 2|975 3,902,862

SHEET 1 [IF 2 ALLOY ll ALLOY B ALLOY C PATENTED 2|975 3,902,862

SHEET 2 BF 2 ALLOY A ALLOY 3 ALL 0) C NICKEL-BASE SUPERALLOY ARTICLES AND METHOD FOR PRODUCING THE SAME Nickel-base superalloys are conventionally used as constructional materials for high-temperature service applications, such as the components for jet engines which are subject during service to high operating temperatures. In many applications the components made from these alloys must exhibit high strength and hardness at elevated temperatures. This is customarily achieved by increasing the alloy content of strengthening elements, such as titanium, aluminum, columbium, tantalum, hafnium, tungsten and molybdenum. However, it has been found that as the alloy content is so increased to achieve the required strength and hardness at elevated temperatures, the alloy becomes increasingly susceptible to chemical segregation which results in an undesirable size and distribution of the hardening constituents which cannot be eliminated during subsequent processing, including forging. In addition, this segregation, during forging and hot working operations, generally promotes cracking with renders fabrication to the desired shapes difficult and expensive. Because of the segregation occurring upon solidification, particularly in components of relatively large mass, a nonuniformity of microstructure and mechanical properties may develop throughout the cross section of the article.

lt has been recognized that the production of nickelbase superalloy components by powder metallurgy, rather than by casting or by casting and working, eliminates many of the problems inherent in casting. Particularly, since the article is not subjected to slow cooling 35 from the molten to the solid state, the article remains homogeneous throughout its cross section. The atomized powder is characterized by a uniform, fine microarticles of this type provide these advantages over casting techniques, it has been found that an undesirable concentration of minor phases, such as carbides, nitrides and the like, at prior particle surfaces or particle 5 boundaries results. This phenomenon renders the product vulnerable to crack propagation, and thus the full strength and ductility of the alloy cannot be realized in the article made therefrom.

It is accordingly a primary object of the present in- 10 vention to provide nickel-base superalloy articles con- This and other objects of the invention, as well as the complete understanding thereof, may be obtained from the following description, specific examples and draw ings, in which FIGS. 1, 2 and 3 are photomicrographs at a magnification of 100X of three compacted powder alloy articles, with the articles of FIGS. 1 and 2 being in accordance with the present invention and with the article of FIG. 3 being outside the scope of the present invention.

FIGS. 4, S and 6 are photographs at a magnification of 15X of the articles of FIGS. 1, 2 and 3, respectively, showing the features of specimens of these articles treated in tension.

It has been found that, in accordance with the present invention, nickel-base superalloys within the composition limits of Table I, in the form of prealloyed powder and compacted to form articles having a density exceeding of theoretical, are characterized by a uniform distribution of minor phases. This, as will be shown hereinafter, provides articles of improved strength and ductility. Consequently, the term fully dense as used herein means a compacted article having a density exceeding 95% of theoretical density.

TABLE I (Percent by weight) Element Broad Preferred Preferred Preferred Preferred Carbon .5 max. .0] to .40 .lS to .25 .01 to .20 .2 to .4 Chromium 10 to l6 l0 to 16 10.5 to 145 I2 to l6 10 to 14 Cobalt 7 to ll 7 to ll 8 to 10 7 to 9 9 to ll Molybdenum Up to 5 l to 5 l to 3 2 5 to 4 5 l to 4 Tungsten Up to 7 2 to 7 3 to 5 2.5 to 4.5 5 to 7 Columbium Up to 5 Up to 5 2.5 to 4.5 Tantalum Up to 5 Up to 5 3 to 5 .5 to 2.5 Hafnium Up to 5 Up to S Tungsten Columbium l to l2 Columbium +Tantalum+ Tantalum Hafnium .5 to 5 Vanadium Up to 5 Up to 5 Titanium l to 5 l to 5 3.2 to 5 L5 to 3.5 2 to 4 Aluminum 2 to 6 2 to 6 2.2 to 4.2 2.5 to 4.5 3.5 to 5.5 Boron .001 to .03 .00l to .03 .001 to .03 .001 to .03 .001 to .03 Zirconium .01 to .20 .01 to .20 .01 to .20 .01 to .20 .01 to .20

Nickel Balance* Balance* Balance* Balance* Balance* *With usual impurities in ordinary amounts structure having a mean intercept boundary (e.g. dendrite arms, cell boundaries and grain boundaries) spacing of 10 microns'maximum as compared to well over microns for the conventionally cast product. This original microstructure of the powder can be substantially maintained in the final compacted article. Al-

though powder metallurgy techniques for producing jet against a stream of the molten metal. The stream is atomized by this action and upon rapid cooling to the solid state the desired prealloyed powder is produced. The powder is then screened to remove undesirably large particles. The powder may then be compacted to form the desired article by any of the well-known compacting techniques, which include hot isostatic pressing, extrusion, forging and rolling. The size of the particles used for compacting in accordance with the present invention typically does not exceed minus 16 mesh US. Standard and generally will not exceed minus 30 mesh.

As a specific example of the practice of the invention three specific nickel-base superalloys were prepared in powder form; these alloys are identified as A, B and C in Table II.

TABLE II EXPERIMENTAL ALLOY COMPOSITIONS Alloys A and B of Table II are within the scope of this invention; whereas, Alloy C is outside the scope of the invention. Prealloyed powder suitable for compacting was prepared from each of the alloys of Table II by melting a charge of the composition under an inert atmosphere, atomizing a stream of the molten metal by striking it with a jet of argon gas and subsequently rapidly cooling the atomized particles to ambient temperature. The powder was collected and screened to minus 100 mesh and loaded in cylindrical mild-steel containers having a height of 9 inches and a diameter of 2.6 inches. The containers were evacuated to remove any moisture present therein and sealed against the atmosphere. The evacuated powder-filled containers were heated to a temperature of 2100F and subjected to isostatic compacting at a pressure of 15,000 psi. This resulted in the powders of each of the alloys being consolidated to a density approaching 100% of theoretical. FIGS. 1, 2 and 3 are photomicrographs, as earlier described, of articles from Alloys A,, B and C, respectively.

It may be readily seen from FIGS. 1 and 2 that the carbides in the articles of Alloys A and B, the compositions of which are within the scope of the present invention, are fine and uniformly distributed throughout the matrix of the article. In contrast, as may be seen from FIG. 3, the carbides in the article from Alloy C, which is a composition outside the scope of this invention, are concentrated at prior particle boundaries. This produces a network of carbides that provides an easy path for propagation of cracks when the article is subjected during service to stress at elevated temperature.

As a demonstration of the improvement obtained by the practice of this invention, articles from Alloys A, B and C were sectioned, heat treated, machined into tensile specimens and tested at room temperature. The results are shown in Table III. It is evident that the strength and ductility of articles from Alloys A and B, which are within the scope of this invention, are superior to those of the article from Alloy C, which is outside the scope of this invention.

TABLE III TENSILE PROPERTIES OF ALLOYS A, B AND C "Heat Tratment 2l00F/4 hr./O.Q. l200F/24 hr./A.C.

1400Fl8 hr/A.C.

2000Fl1 hr./O.Q. 1500F/4 hr./A.C. 1400Fll6 hr./A.C.

1400Fl8 hr./A.C.

"Heat Treatment "Heat Treatment The significance of the improvement with respect to carbide dispersion obtained in accordance with the practice of the invention is demonstrated by FIGS. 4, 5 and 6, which are photographs as earlier described of fractured tensile specimens of the articles of Alloys A, B and C, respectively. The fracture of Alloy C, as shown in FIG. 6, is characterized by the ball and socket type fracture, which indicates fracture propagation along the spherical path of a particle boundary at which minor-phase concentration had occurred. In contrast the fracture of the articles of Alloys A and B, as shown in FIGS. 4 and 5, respectively, occurred randomly, rather than along prior powder particle surfaces.

Although the exact mechanism by which the improved minor phase dispersion is obtained in compacted nickel-base alloy articles produced in accordance with the present invention is not completely understood, it is believed that the inclusion of one or more of the elements columbium, tantalum, hafnium, tungsten and zirconium in the composition serves to stabilize the carbides which form during rapid cooling and solidification of the particles so that subsequent precipitation of carbides at particle boundaries is not produced during heating to elevated temperature incident to compacting.

As a further demonstration of the improved performance of alloys within the scope of this invention, a test specimen was machined from a consolidated powder product of Alloy A and tested in tension at 1950F under a constant head speed of 0.1 in./min. The test temperature selected is representative of that normally used to fabricate nickel-base alloys into useful shapes by forging, extrusion or rolling. The results of the test were as follows:

These results show that the product made in accor-' dance with this invention can be readily hot-formed to the desired useful shapes by virtue of its low resistance to deformation (tensile strength) and outstanding ability to deform withoutfracture (ductility). Whereas, the same alloy produced by conventional means, such as casting, exhibits a very high resistance to deformation (tensile strength 50 ksi) and only limited ability to deform without fracture elongation).

The unique hot workability of the articles of this invention made possible the production of a forging exhibiting mechanical properties which are far superior to those obtainable using techniques of the prior art. Consolidated samples of Alloy A were heated to 2050F and subsequently forged to a 50% reduction in height without cracking. Material cut from the forging was heat treated, machined, and tested in tension. The results are shown in Table IV along with typical values for material produced in accordance with the prior art. It is evident that the products of this invention are consistently superior in both strength and ductility to the product of the prior art.

titanium 1 to 5, aluminum 2 to 6, boron 0.001 to 0.03, zirconium 0.01 to 0.20, balance essentially nickel, said article being characterized by the absence of minor phase concentrations at prior powder-particle boundaries.

2. A nickel-base superalloy compacted, fully dense article produced by elevated-temperature compacting of prealloyed powder particles consisting essentially of, in weight percent, carbon 0.15 to 0.25, chromium 10.5 to 14.5, cobalt 8 to 10, molybdenum l to 3, tungsten. 3 to 5, tantalum 3 to 5, titanium 3.2 to 5, aluminum 2.2 to 4.2, boron 0:00] to 0.03, zirconium 0.01 to 0.20, balance essentially nickel, said article being characterized by the absence of minor phase concentrations at prior powder-particle boundaries.

3. A nickel-base superalloy compacted, fully dense article produced by elevated-temperature compacting of prealloyed powder particles consisting essentially of, in weight percent, carbon 0.01 to 0.20, chromium 12 to 16, cobalt 7 to 9, molybdenum 2.5 to 4.5, tungsten 2.5 to 4.5, columbium 2.5 to 4.5, titanium 1.5 to 3.5, aluminum 2.5 to 4.5, boron 0.001 to 0.03, zirconium 0.01 to 0.20, balance essentially nickel, said article being characterized by the absence of minor phase concentrations at prior powder-particle boundaries.

4. A nickel-base superalloy compacted, fully dense article produced by elevated-temperataure compacting Cast heat treated" We claim:

1. A nickel-base superalloy compacted, fully dense article produced by elevated-temperature compacting of prealloyed powder particles consisting essentially of, in weight percent, carbon 0.01 to 0.40, chromium 10 to 16, cobalt 7 to 11, molybdenum l to 5, tungsten 2 to 7, columbium up to 5, tantalum up to 5, with the total content of columbium tantalum within the range of 0.5 to 5, vanadium up to 5, hafnium up to 5,

of prealloyed powder particles consisting essentially of, in weight percent, carbon 0.2 to 0.4, chromium 10 to 14, cobalt 9 to 11, molybdenum l to 4, tungsten 5 to 7, tantalum 0.5 to 2.5, titanium 2 to 4, aluminum 3.5 to'5.5, boron 0.001 to 0.03, zirconium 0.01 to 0.20, balance essentially nickel, said article being characterized by the absence of minor phase concentrations at prior powder-particle boundaries. 

1. A NICKEL-BASE SUPERALLOY COMPACTED, FULLY DENSE ARTICLE PRODUCED BY ELEVATED-TEMPERATURE COMPACTING OF PREALLOYED POWDER PARTICLES CONSISTING ESSENTIALLY OF, IN WEIGHT PERCENT CARBON 0.01 TO 0.40, CHROMIUM 10 TO 16, COBALT 7 TO 11, MOLYBDENUM 1 TO 5, TUNGSTEN 2 TO 7, COLUBIUM UP TO 5, TANTALUM UP TO 5, WITH THE TOTAL CONTENT OF COLUMBIUM + TANTALUM WITHIN THE RANGE OF 0.5 TO 5, VANDADIUM UP TO 5, HAFNIUM UP TO 5, TITANIUM 1 TO 5, ALUMINUM 2 TO 6, BORON 0.001 TO 0.03, ZIRCONIUM 0.01 TO 0.20, BALANCE ESSENTIALLY NICKEL, SAID ARTICLE CHARACTERIZED BY THE ABSENCE OF MONOR PHASE CONCENTRATIONS AT PIOR POWDER-PARTICLE BOUNDARIES.
 2. A nickel-base superalloy compacted, fully dense article produced by elevated-temperature compacting of prealloyed powder particles consisting essentially of, in weight percent, carbon 0.15 to 0.25, chromium 10.5 to 14.5, cobalt 8 to 10, molybdenum 1 to 3, tungsten 3 to 5, tantalum 3 to 5, titanium 3.2 to 5, aluminum 2.2 to 4.2, boron 0.001 to 0.03, zirconium 0.01 to 0.20, balance essentially nickel, said article being characterized by the absence of minor phase concentrations at prior powder-particle boundaries.
 3. A nickel-base superalloy compacted, fully dense article produced by elevated-temperature compacting of prealloyed powder particles consisting essentially of, in weight percent, carbon 0.01 to 0.20, chromium 12 to 16, cobalt 7 to 9, molybdenum 2.5 to 4.5, tungsten 2.5 to 4.5, columbium 2.5 to 4.5, titanium 1.5 to 3.5, aluminum 2.5 to 4.5, boron 0.001 to 0.03, zirconium 0.01 to 0.20, balance essentially nickel, said article being characterized by the absence of minor phase concentrations at prior powder-particle boundaries.
 4. A nickel-base superalloy compacted, fully dense article produced by elevated-temperataure compacting of prealloyed powder particles consisting essentially of, in weight percent, carbon 0.2 to 0.4, chromium 10 to 14, cobalt 9 to 11, molybdenum 1 to 4, tungsten 5 to 7, tantalum 0.5 to 2.5, titanium 2 to 4, aluminum 3.5 to 5.5, boron 0.001 to 0.03, zirconium 0.01 to 0.20, balance essentially nickel, said article being characterized by the absence of minor phase concentrations at prior powder-particle boundaries. 